libc: silence unsigned->signed warnings with ioctl
This also tweaks cdefs to make __overloadable usable outside of
FORTIFY. It had to be FORTIFY-only before we had unmarked overload
support in clang+Bionic.
Bug: https://github.com/android-ndk/ndk/issues/402
Test: Internal master builds + `mma`. `mma` in Bionic fails if the
change to ioctl is undone.
Change-Id: Ib386b1786e1dca625e6d5a18682005adc734d9c1
diff --git a/libc/include/bits/ioctl.h b/libc/include/bits/ioctl.h
index 0cf87d2..3357c1b 100644
--- a/libc/include/bits/ioctl.h
+++ b/libc/include/bits/ioctl.h
@@ -35,6 +35,28 @@
int ioctl(int __fd, int __request, ...);
+/*
+ * Work around unsigned -> signed conversion warnings: many common ioctl
+ * constants are unsigned.
+ *
+ * Since this workaround introduces an overload to ioctl, it's possible that it
+ * will break existing code that takes the address of ioctl. If such a breakage
+ * occurs, you can work around it by either:
+ * - specifying a concrete, correct type for ioctl (whether it be through a cast
+ * in `(int (*)(int, int, ...))ioctl`, creating a temporary variable with the
+ * type of the ioctl you prefer, ...), or
+ * - defining BIONIC_IOCTL_NO_SIGNEDNESS_OVERLOAD, which will make the
+ * overloading go away.
+ *
+ * FIXME: __has_extension is more or less a clang version check. Remove it when
+ * we don't need to support old clang code.
+ */
+#if defined(__clang__) && __has_extension(overloadable_unmarked) && \
+ !defined(BIONIC_IOCTL_NO_SIGNEDNESS_OVERLOAD)
+/* enable_if(1) just exists to break overloading ties. */
+int ioctl(int __fd, unsigned __request, ...) __overloadable __enable_if(1, "") __RENAME(ioctl);
+#endif
+
__END_DECLS
#endif